ASEXUAL REPRODUCTION. 



191 



tion of special cells, clinging often for a time to the parent, 

 generally dependent for development on union with similar 

 cells of complementary constitution ; we find, in fact, the sexual 

 reproduction which, in the higher organisms, so thoroughly 

 replaces the asexual process. 



§ 4. Occurrence of Asexual Reproduction in Plants and 

 Animals. — In plants, as one would expect from their typical 

 vegetative constitution, the asexual process is common, particu- 

 larly among the lower forms. The most familiar of all cases is 

 afforded by the common liverworts {Marchantia and Lunularia), 



Asexual Propagation of Grass — {a) the bulbils 

 rooting on the ground ; (^) tlieir appear- 

 ance in the inflorescence ; (r) a small 

 portion enlarged. — From nature. 



which through the formation of asexual buds or gemmas in the 

 cups so familiar upon their thallus, are enabled to overrun our 

 flower-pots, and so rapidly become a pest of the greenhouse. 

 Many ferns too, notably among the Aspleniums, reproduce by 

 bulbils, arising upon the frond; and the bulbils which arise in the 

 axils of the leaves of the tiger-lily are familiar missiles for every 

 child accustomed to a flower-garden (see figs. pp. 226 and 287). 

 The alliums, and some of our common grasses also, furnish us 

 with examples of the replacement of flowers by separable buds. 



